Volume control circuit



1941- H. RINIA 2,259,860

' VOLUME CONTROL CIRCUIT Filed Feb. 4, 1939 VOLUME INvENToR.

HERRE R/N/A ATTORNEY.

Patented Oct. 21, 1941 VOLUME CONTROL CIRCUIT Herre Rinia, Eindhoven,Netherlands, assignor, by mesne assignments, to Radio Corporation ofAmerica, New York, N. Y., a corporation of Delaware Application February4, 1939, Serial No. 254,549 In Germany March4, 1938 1 Claim.

The present invention relates to a radio receiver with manual volumecontrol, and preferably with contrast control, wherein the amplificationby the low frequency amplifier is controlled, as is well known, in suchmanner that in the reproduction the ratio between soft and loud passages(the ratio between pianissimo and fortissimo) is increased.

When such an apparatus is adjusted by means of the manual volume controlat a moment when a comparatively soft passage is reproduced with asufiicient sound intensity, the low frequency amplifier of the apparatuswill, in general, be overloaded when loud passages occur. Thisoverloading is still further increased when there is contrast control.

According to the present invention, in order to remove this drawback,there is provided a device having threshold sensitiveness which, if theamplitude of the low frequency oscillations exceeds avpredeterminedvalue, is actuated, and which reduces the amplification of the apparatusby means of an amplification control.

According to one embodiment, the said device controls the bias voltageof at least one electrode of at least one of the amplifying tubes of theapparatus. The control is in this case such that when there occurs 'aloud passage which causes distortion, the amplification is reducedalmost immediately, and is restored comparatively slowly, for examplenot until after one minute, to the initial value.

The invention will be explained more fully with reference to theaccompanying drawing which represents diagrammatically, by way ofexample, a radio receiver according to the invention. That portion ofthis apparatus which precedes the low frequency amplifier is denoted byI. The rectified low frequency oscillations are supplied, through amanual volume control device 2, t the grid of a low frequency amplifyingtube 3. The amplified low frequency oscillations set up across aresistance 4 in the anode circuit of the tube 3 are supplied through acondenser 5 to the network 6 of the low frequency amplifier. The outputcircuit of the latter includes a transformer 1 whose secondary windingis connected to a loudspeaker 8. The low frequency amplifier 6 may beprovided with contrast control which is not shown in detail in thedrawing. The Volume expansion network shown in the drawing is schematic,and is well known to those skilled in the art.

The low frequency oscillations occurring in the output circuit of theamplifier 6 are supplied through a condenser 9 to a rectifier II]. Inthe cathode lead of this rectifier is located a source ll of biasvoltage so that it is not until the amplitude of the low frequencyoscillations in the output circuit of the low frequency amplifier 6exceeds the highest value permissible which corresponds to the value ofthe source of voltage II, that a rectified voltage is produced across aresistance 12. This voltage is applied to the grid of the amplifyingtube 3 in such manner that the amplification is decreased to a value atwhich the amplifier is not overloaded.

The rectifier I0 is so chosen that when the threshold value is surpassedthe current flowing through the rectifier charges the condenser 9 veryrapidly so that an almost immediate control of the amplification of tube3 is obtained. The condenser 9 and the resistance I2 are so chosen thatthe discharge of the condenser 9 takes place comparatively slowlythrough resistance l2, so that, for example, only after one minute theamplification by the tube 3 is restored to the initial value.

What is claimed is:

In combination with a source of audio voltage, an audio amplifier tubehaving at least a cathode, control grid and output electrode, meansconnecting said cathode to a point of relatively fixed potential, aresistive path connected across said source, a resistor in series withsaid path and connected to said point, a slider element connecting saidgrid to said path to provide a manually adjustable volume controldevice, an audio utilization network connected to said output electrode,an audio volume expansion network operatively associated with saidutilization network, means to protect said amplifier against overloadingdue to audio voltages above a predetermined amplitude produced by actionof said expansion network, said last means comprising a rectifier devicein circuit with said resistor to develop across the latterunidirectional voltage for biasing said grid in an amplifiergainreducing sense, means for maintaining the rectifier ineffective foraudio voltages below said amplitude, a condenser coupling saidutilization network to said rectifier, said rectifier being constructedto charge said condenser relatively quickly in response to said audiovoltage exceeding said amplitude, and said resistor andcondenser beingso chosen as to prevent rapid discharge of said condenser.

I-IERRE RINIA.

